1. Field of the Invention
An embodiment of the present invention relates to a method for manufacturing a substrate in which a semiconductor layer is provided over an insulating layer. In addition, an embodiment of the present invention relates to a method for manufacturing a semiconductor device by using a substrate in which a semiconductor layer is provided over an insulating layer.
2. Description of the Related Art
In recent years, an integrated circuit using an SOI (silicon on insulator) substrate in which a thin single crystal semiconductor layer is formed over an insulating surface, instead of a bulk silicon wafer, has been developed. With the use of an SOI substrate, parasitic capacitance between a drain of a transistor and a substrate can be reduced; thus, an SOI substrates is attracting attention for its ability to improve performance of a semiconductor integrated circuit.
One of known methods for manufacturing an SOI substrate is a hydrogen ion implantation separation method (for example, see Patent Document 1). A summary of a method for manufacturing an SOI substrate by a hydrogen ion implantation separation method is as follows. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method to form a microbubble layer at a predetermined depth from a surface. Next, the silicon wafer into which hydrogen ions have been implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. Then, heat treatment is performed. The microbubble layer serves as a cleavage plane and part of the silicon wafer into which hydrogen ions have been implanted is separated into a thin film shape along the microbubble layer. Accordingly, a single crystal silicon film can be formed over the other silicon wafer to which the silicon wafer into which hydrogen ions have been implanted is bonded.
In addition, a method for forming a single crystal silicon film over a base substrate made of glass by using such a hydrogen ion implantation separation method as described above has been proposed (for example, see Patent Document 2). Since a glass substrate can have a larger area and is less expensive than a silicon wafer, by using a glass substrate as a base substrate, an inexpensive large-sized SOI substrate can be manufactured.
Further, in Patent Document 2, it is disclosed that a silicon nitride film is provided between the base substrate and the single crystal silicon film so as to prevent impurities or the like contained in the base substrate from being diffused to the single crystal silicon film.
A single crystal semiconductor substrate is irradiated with accelerated hydrogen ions, whereby implantation of the hydrogen ions or doping with the hydrogen ions is performed on part of the single crystal semiconductor substrate at a predetermined depth to form an embrittled region there. Then, heat treatment is performed. Through the heat treatment, hydrogen contained in the embrittled region is vaporized and further the hydrogen is expanded, so that a cleavage plane is formed in the embrittled region.